WHOLE ROCK K/Ar VS. ZIRCON U/Pb AGES FOR THE UPPER CRETACEOUS MAGMATIC ROCKS (BANATITE) ASSOCIATED TO GOSAU-TYPE BASINS LĂPUGIU AND RUSCA MONTANĂ (W ROMANIA)

This study comprises 12 new K/Ar data on Upper Cretaceous intrusive and volcaniclastic deposits associated to Gosau-type basins Lăpugiu and Rusca Montană (South Carpathians, W Romania). Here we validate K/Ar as a useful method for age determination of Upper Cretaceous rocks, those that in the absence of zircon cannot be dated by U-Pb methodologies. The K-Ar age determinations fall within the age range of the known zircon U-Pb method, i.e. 83-70 Ma. We found that the age of volcaniclastic sequences or subvolcanic rocks is always younger (~70-76 Ma) than the associated hypabyssic intrusive rocks (~80-83 Ma). We suggest that 70-80 Ma may corresponds to a period with extensional tectonics and Gosau basins generation.